U.S. patent application number 12/407434 was filed with the patent office on 2009-09-24 for apparatus and method for encoding and decoding using bandwidth extension in portable terminal.
This patent application is currently assigned to Samsung Electronics Co. Ltd.. Invention is credited to Chul-Yong AHN, Pavel MARTYNOVICH, Geun-Bae SONG.
Application Number | 20090240509 12/407434 |
Document ID | / |
Family ID | 41089764 |
Filed Date | 2009-09-24 |
United States Patent
Application |
20090240509 |
Kind Code |
A1 |
SONG; Geun-Bae ; et
al. |
September 24, 2009 |
APPARATUS AND METHOD FOR ENCODING AND DECODING USING BANDWIDTH
EXTENSION IN PORTABLE TERMINAL
Abstract
An apparatus and method for encoding and decoding using mutual
information between a high band signal and a low band signal to
increase a coding efficiency in a portable terminal are provided.
The apparatus includes a bandwidth extender for extracting
auxiliary information relating to a characteristic of a high band
signal using the high band signal and a low band signal and an
encoder for encoding residual high band signal obtained by
subtracting auxiliary information acquired from the low band signal
from auxiliary information acquired from the high band signal.
Inventors: |
SONG; Geun-Bae; (Jecheon-si,
KR) ; MARTYNOVICH; Pavel; (Suwon-si, KR) ;
AHN; Chul-Yong; (Suwon-si, KR) |
Correspondence
Address: |
Jefferson IP Law, LLP
1730 M Street, NW, Suite 807
Washington
DC
20036
US
|
Assignee: |
Samsung Electronics Co.
Ltd.
Suwon-si
KR
|
Family ID: |
41089764 |
Appl. No.: |
12/407434 |
Filed: |
March 19, 2009 |
Current U.S.
Class: |
704/500 ;
704/E21.001 |
Current CPC
Class: |
G10L 21/038 20130101;
G10L 19/0204 20130101; G10L 19/24 20130101 |
Class at
Publication: |
704/500 ;
704/E21.001 |
International
Class: |
G10L 21/00 20060101
G10L021/00 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 20, 2008 |
KR |
10-2008-0025980 |
Mar 21, 2008 |
KR |
10-2008-0026340 |
Claims
1. A coding apparatus using a band extension, the coding apparatus
comprising: a bandwidth extender for extracting auxiliary
information relating to a characteristic of a high band signal
using the high band signal and a low band signal; and an encoder
for encoding a residual high band signal obtained by subtracting
auxiliary information acquired from the low band signal from
auxiliary information acquired from the high band signal.
2. The coding apparatus of claim 1, wherein the bandwidth extender
acquires the auxiliary information from the low band signal using
past pre-coded high band auxiliary information and auxiliary
information acquired from the low band signal.
3. The coding apparatus of claim 1, further comprising: a filter
factor calculator for, after the low band signal is encoded,
determining filter factors to increase mutual information of the
high band signal and the encoded low band signal; a high band
mutual information filter for processing to increase the mutual
information of the high band signal using the determined filter
factors; and a low band mutual information filter for processing to
increase the mutual information of the low band signal using the
determined filter factors.
4. The coding apparatus of claim 3, further comprising: a high band
estimator for estimating a high band signal using the low band
signal of the increased mutual information and for processing to
output a residual high band signal by subtracting the estimated
high band signal and the high band signal of the increased mutual
information; and a quantizer for quantizing and outputting the
residual high band signal.
5. The coding apparatus of claim 3, wherein the filter factors for
increasing the mutual information reproduce an original signal Y
from a converted signal Y2, establish the mutual information
I[X;Y2]>I[X;Y], and make a dynamic range of Y2 not be greater
than at least a dynamic range of Y in a statistical sense, where X
denotes the low band signal, Y denotes the high band signal, H[ ]
denotes the high band mutual information filter, H.sup.-1[ ]
denotes a high band mutual information inverse filter, and Y2
denotes a high band signal converted by H[ ].
6. The coding apparatus of claim 3, wherein the filter factors for
increasing the mutual information are determined using a decoded
high band signal and a decoded low band signal.
7. The coding apparatus of claim 3, wherein the mutual information
of one of the high band signal and the low band signal is
increased.
8. A coding method using a band extension, the coding method
comprising: extracting auxiliary information relating to a
characteristic of a high band signal using the high band signal and
a low band signal; subtracting auxiliary information, acquired from
the low band signal, from auxiliary information acquired from the
high band signal; and encoding the subtracted residual high band
signal.
9. The coding method of claim 8, further comprising acquiring the
auxiliary information from the low band signal using past pre-coded
high band auxiliary information and auxiliary information acquired
from the low band signal.
10. The coding method of claim 8, further comprising: after the low
band signal is encoded, determining filter factors to increase
mutual information of the high band signal and the encoded low band
signal; and converting a signal using the increased mutual
information of the high band signal and the low band signal using
the determined filter factors.
11. The coding method of claim 10, further comprising: estimating a
high band signal using the low band signal of the increased mutual
information; outputting a residual high band signal from which the
estimated high band signal and the high band signal of the
increased mutual information are subtracted; and transmitting the
output residual high band signal.
12. The coding method of claim 10, wherein the filter factors for
increasing the mutual information reproduce an original signal Y
from a converted signal Y2, establish the mutual information
I[X;Y2]>I[X;Y], and make a dynamic range of Y2 not be greater
than at least a dynamic range of Y in a statistical sense, where X
denotes the low band signal, Y denotes the high band signal, H[ ]
denotes the high band mutual information filter, H.sup.-1[ ]
denotes a high band mutual information inverse filter, and Y2
denotes a high band signal converted by H[ ].
13. The coding method of claim 10, wherein the filter factors for
increasing the mutual information are determined using a decoded
high band signal and a decoded low band signal.
14. The coding method of claim 10, wherein the mutual information
of one of the high band signal and the low band signal is
increased.
15. A coding apparatus comprising: a predictor for estimating a
high band signal using a pre-decoded high band signal; a bandwidth
extender for receiving an encoded low band signal and for
estimating a high band signal using the received encoded low band
signal; a low band encoder for encoding a received low band signal
and for providing the encoded low band signal to the bandwidth
extender; and an encoder for providing an encoded high band
signal.
16. The coding apparatus of claim 15, further comprising a first
subtractor for generating a first residual high band signal by
subtracting the estimated high band signal of the predictor from
the pre-decoded high band signal.
17. The coding apparatus of claim 16, further comprising a second
subtractor for generating a second residual high band signal by
subtracting the estimated high band signal of the bandwidth
extender from the first residual high band signal.
18. The coding apparatus of claim 17, wherein the encoder encodes
the second residual high band signal.
Description
[0001] This application claims the benefit under 35 U.S.C.
.sctn.119(a) of a Korean patent application filed in the Korean
Intellectual Property Office on Mar. 20, 2008 and assigned Serial
No. 10-2008-0025980 and a Korean patent application filed in the
Korean Intellectual Property Office on Mar. 21, 2008 and assigned
Serial No. 10-2008-0026340 the entire disclosure of both of which
are hereby incorporated by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates generally to an apparatus and
a method for encoding and decoding in a portable terminal. More
particularly, the present invention relates to an apparatus and a
method for enhancing a coding efficiency in a portable terminal
which adopts a bandwidth extension.
[0004] 2. Description of the Related Art
[0005] With advances in digital signal processing technology, audio
signals are typically stored and reproduced as digital data. A
digital audio storing/reproducing apparatus samples and quantizes
an analog audio signal, converts the analog signal into a digital
audio data using Pulse Code Modulation (PCM), and stores the
digital data to an information storage medium such as Compact Disc
(CD) or Digital Versatile Disc (DVD). Because the data is
conveniently stored, a user may reproduce the audio data on
demand.
[0006] In comparison to other methods, the digital method provides
an enhanced sound quality. For example, compared to a method which
estimates and restores a high band signal from a low band signal or
a feature vector extracted from the low band signal that reproduces
only the low band signal at the receiver using an artificial
BandWidth Extension (BWE), the sound quality of the digital method
is enhanced.
[0007] As an example of a receiver using BWE, provided that a
sampling frequency Fs of an input signal is 16 kHz, the bandwidth
extension restores the high band signal of 4 k.about.8 kHz from the
low band signal of 0.about.4 kHz and produces the same signal 16
kHz as the original input signal. The success of the bandwidth
extension is closely related with a correlation between the
frequency bands (the high band and the low band) of the input
signal.
[0008] When the input signal of one frame is divided into the low
band and the high band based on the frequency band, the signals of
the two bands have a close correlation because they are generated
from the same source. If the correlation or mutual information
between the two bands is considerable, the high band signal
recovered through the bandwidth extension exhibits sound quality
that is close to the original sound.
[0009] However, when there is only a small amount of information
relating to the high band signal because of a low correlation
between the two bands, the bandwidth extension cannot adequately
restore the high band signal.
[0010] Accordingly, there is a need for an improved apparatus and a
method for enhancing performance of a coding apparatus using a
bandwidth extension in a portable terminal.
SUMMARY OF THE INVENTION
[0011] An aspect of the present invention is to address at least
the above mentioned problems and/or disadvantages and to provide at
least the advantages described below. Accordingly, an aspect of the
present invention is to provide an apparatus and a method for
enhancing a performance of the coding apparatus using a BandWidth
Extension (BWE) in a portable terminal.
[0012] Another aspect of the present invention is to provide an
apparatus and a method for coding by removing high band information
overlapping with a low band signal in the coding apparatus using a
BWE in a portable terminal.
[0013] Yet another aspect of the present invention is to provide an
apparatus and a method for coding by removing a correlation between
frames in the coding apparatus using a BWE in a portable
terminal.
[0014] According to an aspect of the present invention, a coding
apparatus using band extension is provided. The apparatus includes
a bandwidth extender for extracting auxiliary information relating
to a characteristic of a high band signal using the high band
signal and a low band signal and an encoder for encoding a residual
high band signal obtained by subtracting auxiliary information
acquired from the low band signal from auxiliary information
acquired from the high band signal.
[0015] According to another aspect of the present invention, a
coding method is provided. The method includes extracting auxiliary
information relating to a characteristic of a high band signal
using the high band signal and a low band signal, subtracting
auxiliary information acquired from the low band signal from
auxiliary information acquired from the high band signal, and
encoding the subtracted residual high band signal.
[0016] Other aspects, advantages, and salient features of the
invention will become apparent to those skilled in the art from the
following detailed description, which, taken in conjunction with
the annexed drawings, discloses exemplary embodiments of the
invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] The above and other aspects, features and advantages of
certain exemplary embodiments the present invention will be more
apparent from the following description taken in conjunction with
the accompanying drawings, in which:
[0018] FIG. 1 is a block diagram of a coding apparatus according to
an exemplary embodiment of the present invention;
[0019] FIG. 2 is a block diagram of a bandwidth extender of a
coding apparatus according to an exemplary embodiment of the
present invention;
[0020] FIG. 3 is a flowchart of a method for increasing coding
efficiency using auxiliary information indicative of a
characteristic of a high band signal at an encoder according to an
exemplary embodiment of the present invention;
[0021] FIG. 4 is a flowchart of a method for increasing coding
efficiency using auxiliary information indicative of a
characteristic of a high band signal at a decoder according to an
exemplary embodiment of the present invention;
[0022] FIG. 5 is a block diagram of a coding apparatus according to
an exemplary embodiment of the present invention;
[0023] FIG. 6A is a graph of mutual information between the low
band signal and the high band signal;
[0024] FIG. 6B is a graph of coding efficiency of the coding
apparatus using BandWidth Extension and Scaler Quantizer
(BWE+SQ);
[0025] FIG. 6C is a graph of coding efficiency of the coding
apparatus using BandWidth Extension and Vector Quantizer
(BWE+VQ);
[0026] FIG. 7 is a block diagram of a coding apparatus according to
an exemplary embodiment of the present invention;
[0027] FIG. 8 is a block diagram of a bandwidth extender of a
coding apparatus according to an exemplary embodiment of the
present invention;
[0028] FIG. 9 is a flowchart for increasing coding efficiency by
predicting a high band signal at an encoder according to an
exemplary embodiment of the present invention;
[0029] FIG. 10 is a flowchart for increasing coding efficiency by
predicting a high band signal at a decoder according to an
exemplary embodiment of the present invention;
[0030] FIG. 11A is a graph illustrating performance of a coding
apparatus using serial Predictive Vector Quantization and BandWidth
Extension (serial PVQ+BWE) according to an exemplary embodiment of
the present invention;
[0031] FIG. 11B is a graph illustrating performance of a coding
apparatus using parallel Predictive Vector Quantization and
BandWidth Extension (parallel PVQ+BWE) according to an exemplary
embodiment of the present invention;
[0032] FIG. 12 is a block diagram of an encoder of a portable
terminal according to an exemplary embodiment of the present
invention;
[0033] FIG. 13 is a block diagram of a decoder of a portable
terminal according to an exemplary embodiment of the present
invention;
[0034] FIG. 14 is a block diagram of a filter factor calculator of
an encoder according to an exemplary embodiment of the present
invention;
[0035] FIG. 15 is a block diagram of a filter factor calculator of
a decoder according to an exemplary embodiment of the present
invention;
[0036] FIG. 16 is a flowchart illustrating operations of an encoder
according to an exemplary embodiment of the present invention;
[0037] FIG. 17 is a flowchart illustrating operations of a decoder
according to an exemplary embodiment of the present invention;
[0038] FIG. 18 is a flowchart of a method for determining filter
factors at a filter factor calculator according to an exemplary
embodiment of the present invention;
[0039] FIG. 19A is a graph comparing performance of a coding
apparatus employing only a high band mutual information filter
according to an exemplary embodiment of the present invention and a
conventional coding apparatus; and
[0040] FIG. 19B is a graph comparing performance of a coding
apparatus employing only a low band mutual information filter
according to an exemplary embodiment of the present invention and a
conventional coding apparatus
[0041] Throughout the drawings, like reference numerals will be
understood to refer to like parts, components and structures.
DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS
[0042] The following description with reference to the accompanying
drawings is provided to assist in a comprehensive understanding of
exemplary embodiments of the present invention as defined by the
claims and their equivalents. It includes various specific details
to assist in that understanding but these are to be regarded as
merely exemplary. Accordingly, those of ordinary skill in the art
will recognize that various changes and modifications of the
embodiments described herein can be made without departing from the
scope and spirit of the invention. Also, descriptions of well-known
functions and constructions are omitted for clarity and
conciseness.
[0043] The terms and words used in the following description and
claims are not limited to the bibliographical meanings, but, are
merely used by the inventor to enable a clear and consistent
understanding of the invention. Accordingly, it should be apparent
to those skilled in the art that the following description of
exemplary embodiments of the present invention are provided for
illustration purpose only and not for the purpose of limiting the
invention as defined by the appended claims and their
equivalents.
[0044] It is to be understood that the singular forms "a," "an,"
and "the" include plural referents unless the context clearly
dictates otherwise. Thus, for example, reference to "a component
surface" includes reference to one or more of such surfaces.
[0045] By the term "substantially" it is meant that the recited
characteristic, parameter, or value need not be achieved exactly,
but that deviations or variations, including for example,
tolerances, measurement error, measurement accuracy limitations and
other factors known to skill in the art, may occur in amounts that
do not preclude the effect the characteristic was intended to
provide.
[0046] Exemplary embodiments of the present invention provide an
apparatus and a method for enhancing a coding performance in a
portable terminal using a bandwidth extension.
[0047] FIG. 1 is a block diagram of a coding apparatus according to
an exemplary embodiment of the present invention.
[0048] An exemplary coding apparatus of the present invention
extracts and codes information relating to a characteristic of a
high band signal and prevents redundancy of high band information
using a low band signal. The coding apparatus includes an encoder
100 and a decoder 110.
[0049] The coding apparatus extracts auxiliary information relating
to the characteristic of the high band signal using the high band
signal and the low band signal. The coding apparatus also controls
to encode residual high band auxiliary information generated by
subtracting the auxiliary information extracted using the low band
signal from the auxiliary information extracted using the high band
signal at a subtractor.
[0050] When receiving the residual high band auxiliary information,
the coding apparatus decodes the received auxiliary information and
confirms the high band auxiliary information using the decoded low
band signal. Next, the coding apparatus controls an adder to add
the confirmed auxiliary information and output the original high
band signal.
[0051] While the overall operation of the coding apparatus has been
described above, the operations of the coding apparatus are
explained in further detail below.
[0052] Referring to FIG. 1, the encoder 100 of the coding apparatus
includes a high band auxiliary information extractor 101, a
residual high band auxiliary information encoder 103, a bandwidth
extender 105, and a low band encoder 107.
[0053] The high band auxiliary information extractor 101 extracts
auxiliary information which relates to the characteristic of the
high band signal to produce the original input signal using a
correlation between the high band and the low band. Herein, the
auxiliary information represents the characteristic of the high
band signal, such as a Linear Prediction Coefficient (LPC)
representing the shape of the envelope of the high band frequency,
a Mel-Frequency Cepstral Coefficient (MFCC) of a similar type,
energy of the high band and the like.
[0054] The low band encoder 107 encodes the low band signal of the
signal input through a band pass filter (not shown) and provides
the encoded low band signal to the bandwidth extender 105.
[0055] The bandwidth extender 105 receives the low band signal
encoded by the low band encoder 107 and estimates high band
auxiliary information.
[0056] The residual high band auxiliary information encoder 103
encodes residual high band auxiliary information which includes
auxiliary information of the high band, from which the subtractor
of the coding apparatus subtracts the auxiliary information
extracted using the low band signal. Herein, the residual high band
auxiliary information indicates auxiliary information from which a
redundant part of the auxiliary information extracted using the low
band is eliminated when the high band auxiliary information is
encoded, to prevent the redundant encoding of the partial
information of the high band estimated from the low band
information when the auxiliary information is extracted and encoded
in the low band and the high band according to the general
bandwidth extension.
[0057] The decoder 110 of the coding apparatus extracts high band
auxiliary information by decoding the encoded residual high band
auxiliary information and the encoded low band auxiliary
information, adds the extracted auxiliary information, and outputs
a reproduction of the original high band signal. The decoder 110
includes an auxiliary information decoder 111, a bandwidth extender
113, and a low band decoder 115.
[0058] The low band decoder 115 reproduces the low band signal by
decoding the encoded low band information received over a
communication channel.
[0059] The bandwidth extender 113 estimates high band auxiliary
information using the low band signal decoded by the low band
decoder 115. The auxiliary information decoder 111 generates
residual high band auxiliary information by decoding the encoded
residual high band auxiliary information.
[0060] FIG. 2 is a block diagram of a bandwidth extender of a
coding apparatus according to an exemplary embodiment of the
present invention.
[0061] The bandwidth extender of FIG. 2 includes a bandwidth
extender 200 of the encoder and a bandwidth extender 210 of the
decoder.
[0062] The bandwidth extender 200 of the encoder extracts the
auxiliary information of the high band using the encoded low band
signal. The bandwidth extender 200 includes a statistical model
201, a BandWidth Extension (BWE) estimator 203, a feature vector
extractor 205, and a low band decoder 207.
[0063] The bandwidth extender 200 of the encoder decodes the
encoded low band signal using the low band decoder 207 and applies
the decoded low band signal to the feature vector extractor 205.
The feature vector extractor 205 generates a feature vector of the
input low band signal and provides the generated feature vector to
the BWE estimator 203.
[0064] The BWE estimator 203 estimates high band auxiliary
information using the input low band feature vector and the
statistical model 201 and outputs the estimated high band auxiliary
information. Herein, the statistical model 201 may include preset
information used for the BWE estimation.
[0065] In an exemplary implementation in which the high band
auxiliary information is in a scalar form, the estimated high band
auxiliary information and the residual high band auxiliary
information are in the scalar form as well. Accordingly, the
residual high band auxiliary information encoder employs a Scalar
Quantizer (SQ). In a case of the vector type, the residual high
band auxiliary information encoder employs a Vector Quantizer
(VQ).
[0066] The encoder generates the residual high band auxiliary
information by subtracting the auxiliary information estimated by
the bandwidth extender 200 from the auxiliary information extracted
using the high band signal.
[0067] The bandwidth extender 210 of the decoder estimates the high
band auxiliary information from the input low band signal. The
bandwidth extender 210 includes a statistical model 211, a BWE
estimator 213, and a feature vector extractor 215, which are
substantially the same as those in the bandwidth extender 200 of
the encoder.
[0068] The bandwidth extender 210 of the decoder inputs the low
band signal to the feature vector extractor 215. The feature vector
extractor 215 generates a feature vector of the input low band
signal and applies the feature vector to the BWE estimator 213.
[0069] The BWE estimator 213 estimates the high band auxiliary
information using the input low band feature vector and the
statistical model 211 and outputs the estimated high band auxiliary
information. Herein, the statistical model 211 may include preset
information required for the BWE estimation.
[0070] FIG. 3 is a flowchart of a method for increasing coding
efficiency using auxiliary information indicative of a
characteristic of a high band signal at an encoder according to an
exemplary embodiment of the present invention.
[0071] After extracting high band auxiliary information (hereafter,
referred to as first auxiliary information) from the input signal
in step 301, the encoder processes to extract the high band
auxiliary information (hereafter, referred to as second auxiliary
information) using the low band signal in step 303. Herein, the
high band auxiliary information relates to the characteristic of
the high band signal to produce the original input signal using the
correlation between the high band and the low band, such as LPC
representing the shape of the envelope of the high band frequency,
MFCC of the similar type, energy of the high band and the like.
[0072] After generating the residual high band auxiliary
information by subtracting the second auxiliary information from
the first auxiliary information in step 305, the encoder processes
to encode and transmit the generated residual high band auxiliary
information in step 307. Herein, the residual high band auxiliary
information is produced by removing the second auxiliary
information from the input high band auxiliary information.
[0073] Next, the encoder finishes this process.
[0074] FIG. 4 is a flowchart of a method for increasing coding
efficiency using auxiliary information indicative of a
characteristic of a high band signal at a decoder according to an
exemplary embodiment of the present invention.
[0075] In the following description, it is assumed that the decoder
decodes and outputs the low band signal received from an
encoder.
[0076] After receiving the encoded residual high band signal from
the encoder in step 401, the decoder generates first auxiliary
information by decoding the received residual high band signal in
step 403.
[0077] In step 405, the decoder confirms the high band information
(hereafter, referred to as second auxiliary information) from the
low band signal.
[0078] After adding the first auxiliary information and the second
auxiliary information in step 407, the decoder produces the
original high band signal using the added high band information in
step 409 and then finishes this process.
[0079] FIG. 5 is a block diagram of a coding apparatus according to
an exemplary embodiment of the present invention.
[0080] The coding apparatus of FIG. 5 prevents redundancy of the
high band information using the low band signal by extracting and
encoding the information relating to the characteristic of the high
band signal as described in FIG. 1. For estimating the high band
auxiliary information, the coding apparatus feeds back and utilizes
not only the low band signal but also the past pre-encoded high
band auxiliary information.
[0081] Referring to FIG. 5, the coding apparatus extracts the
auxiliary information relating to the characteristic of the high
band signal by use of the high band signal and the low band signal.
The coding apparatus extracts the auxiliary information by feeding
back the past pre-encoded high band auxiliary information 501.
[0082] The coding apparatus encodes the residual high band
auxiliary information generated by subtracting the auxiliary
information extracted using the low band signal from the auxiliary
information extracted using the high band signal.
[0083] When receiving the residual high band auxiliary information,
the coding apparatus decodes the received auxiliary information and
confirms the high band auxiliary information using the decoded low
band signal. In so doing, the coding apparatus processes to output
the original high band signal using not only the low band signal
but also the auxiliary information 510 using the fed back high band
auxiliary information.
[0084] While the overall operation of the coding apparatus has been
described above, it is described in further detail below.
[0085] An exemplary encoder of the coding apparatus may include a
high band auxiliary information extractor, a residual high band
auxiliary information encoder, a bandwidth extender, and a low band
decoder as mentioned in FIG. 1. The high band auxiliary information
extractor, the residual high band auxiliary information encoder,
and the low band encoder operate substantially the same as in FIG.
1 and therefore shall not be further explained.
[0086] The bandwidth extender extracts the auxiliary information by
feeding back the low band signal encoded by the low band encoder
and the past pre-encoded high band auxiliary information.
[0087] The encoder processes to encode the residual high band
auxiliary information which is the auxiliary information of the
high band obtained by subtracting the auxiliary information
extracted using the low band signal and the pre-encoded high band
auxiliary information at the subtractor of the coding
apparatus.
[0088] The decoder of the coding apparatus extracts the high band
auxiliary information by decoding the encoded residual high band
auxiliary information and the encoded low band auxiliary
information, adds the extracted auxiliary information, and thus
produces the original high band signal. The decoding can include an
auxiliary information decoder, a bandwidth extender, and a low band
decoder.
[0089] The low band decoder reproduces the low band signal by
decoding the encoded low band information received over the
communication channel.
[0090] The bandwidth extender estimates the high band auxiliary
information using the low band signal decoded by the low band
decoder and the fed back high band auxiliary information. The
auxiliary information decoder generates the residual high band
auxiliary information by decoding the encoded residual high band
auxiliary information.
[0091] FIG. 6 includes graphs illustrating performance of a coding
apparatus according to an exemplary embodiment of the present
invention.
[0092] In FIG. 6, performance of the coding apparatus is determined
by the mutual information between the low band signal and the high
band signal.
[0093] The mutual information between the low band signal and the
high band signal can be acquired based on Equation (1).
I ( X ; Y ) = .intg. .OMEGA. y .intg. .OMEGA. x f XY ( X , Y ) log
2 ( f XY ( X , Y ) f X ( X ) f y ( Y ) ) x y ( 1 ) ##EQU00001##
[0094] In Equation (1), X denotes a feature vector of the low band
signal and Y denotes a feature vector of the high band signal.
f.sub.X(x) denotes a probability density function of X, f.sub.Y(y)
denotes a probability density function of Y, and f.sub.XY(x, y)
denotes a joint probability density function of X and Y.
[0095] In an exemplary implementation, the coding apparatus uses
the 10.sup.th order MFCC. That is, X={X1, . . . , X10} as the
feature vector for the low band signal and uses the 8.sup.th order
MFCC, that is, Y={Y1, . . . , Y8} as the feature vector for the
high band signal. Instead of the MFCC, another feature vector, such
as LPC, can be selected in various applications.
[0096] The coding apparatus can define the mutual information
between the components of the low band vector X and the high band
vector Y as shown in Table 1, and define the mutual information
between sub-vectors of the low band vector X and the high band
vector Y as shown in Table 2.
TABLE-US-00001 TABLE 1 [X; Y component] MI (bit) [X; Y1]
1.214624121 [X; Y2] 0.442184563 [X; Y3] 0.403603817 [X; Y4]
0.301242604 [X; Y5] 0.197981724 [X; Y6] 0.160667332 [X; Y7]
0.150365385 [X; Y8] 0.124140187
TABLE-US-00002 TABLE 2 [X; Y sub-vector] MI (bit) [X; Y1]
1.214624121 [X; Y1, Y2] 1.553642011 [X; Y1, . . . , Y3] 1.863667033
[X; Y1, . . . , Y4] 2.078319061 [X; Y1, . . . , Y5] 2.21684601 [X;
Y1, . . . , Y6] 2.340196486 [X; Y1, . . . , Y7] 2.437012574 [X; Y]
2.513291974
[0097] FIG. 6A is a graph of mutual information between the low
band signal and the high band signal.
[0098] The mutual information can be represented as shown in FIG.
6A. When a coding apparatus according to an exemplary embodiment of
the present invention encodes the high band 8.sup.th order MFCC as
shown in FIG. 6A, the scalar quantization can exhibit coding
efficiency of about 4.5 bits (the sum of the second column of Table
1) per frame and the vector quantization can exhibit coding
efficiency of about 2.5 bits (the MI value of [X; Y] of Table 2)
per frame. Given the frame size of 20 ms, those bit efficiencies
per frame correspond to 225 bits and 125 bits per second.
[0099] The coding apparatus may achieve the coding performance as
shown in Table 3 and Table 4.
TABLE-US-00003 TABLE 3 Quantization bits BWE + SQ (CD value) SQ (CD
value) 0 0.22716 0.998309 1 0.103151 0.332132 2 0.036519 0.085834 3
0.011267 0.022771 4 0.003119 0.006094 5 0.000827 0.001615 6
0.000213 0.000419 7 5.4E-05 0.000107 8 1.34E-05 2.72E-05
[0100] CD denotes the Cepstral Distance value.
TABLE-US-00004 TABLE 4 Quantization bits BWE + VQ (CD value) VQ (CD
value) 0 0.759873 1.000935 1 0.692462 0.886891 2 0.608997 0.766667
3 0.528997 0.651902 4 0.453339 0.55646 5 0.389293 0.472844 6
0.33218 0.400793 7 0.283245 0.34054 8 0.24111 0.288309
[0101] CD denotes the Cepstral Distance value.
[0102] Table 3 compares the coding efficiency obtained by the
method for coding the high band vector component Y1 using the SQ
and the method for coding the high band vector component Y1 using
the BWE based coder (BWE+SQ). Table 4 compares the coding
efficiency obtained by the method for coding the high band vector Y
using the VQ and the method for coding the high band vector Y using
the BWE based coder (BWE+VQ). The coding efficiency of the coding
apparatus is shown in FIGS. 6B and 6C.
[0103] FIG. 6B is a graph of coding efficiency of the coding
apparatus using (BWE+SQ) and FIG. 6C is a graph of coding
efficiency of the coding apparatus using (BWE+VQ).
[0104] In FIGS. 6B and 6C, the efficiency is notable in the coding
at low bits. The scalar quantization increases the coding
efficiency by about 1.5 bits per frame at maximum and the vector
quantization increases the coding efficiency by about 2 bits per
frame at maximum.
[0105] FIG. 7 is a block diagram of a coding apparatus according to
an exemplary embodiment of the present invention.
[0106] The coding apparatus of FIG. 7 enhances the coding
performance using prediction information which predicts the signal
of the high band. The coding apparatus includes an encoder 700 and
a decoder 710.
[0107] The coding apparatus predicts the high band signal using the
pre-decoded high band signal and generates the residual high band
signal by subtracting the predicted high band signal (the
correlation between the frames) from the input high band signal.
Next, the encoder predicts the high band signal (the correlation in
the frame) using the encoded low band signal and processes to
encode the signal by subtracting the predicted high band signal
from the residual high band signal.
[0108] The decoder corresponding to the encoder decodes the
received signal and confirms the high band signal using the decoded
low band signal. Next, the coding apparatus processes to produce
the original high band signal by adding the confirmed high band
signals.
[0109] While the overall operation of the coding apparatus has been
described, more detailed descriptions on the coding apparatus are
now provided.
[0110] Referring to FIG. 7, the encoder 700 of the coding apparatus
includes a predictor 701, an encoder 703, a bandwidth extender 705,
and a low band encoder 707.
[0111] The predictor 701 of the encoder 700 estimates the high band
signal using the pre-decoded high band signal.
[0112] The low band encoder 707 encodes the low band signal of the
input signal and provides the encoded low band signal to the
bandwidth extender 705.
[0113] The bandwidth extender 705 receives the low band signal
encoded by the low band encoder 707 and estimates the high band
signal.
[0114] The encoder 703 encodes the residual high band signal which
is the high band signal from which subtractors of the coding
apparatus subtract the high band signal estimated using the low
band signal.
[0115] The decoder 710 of the coding apparatus includes a decoder
711, a predictor 713, a bandwidth extender 715 and a low band
decoder 717.
[0116] FIG. 8 is a block diagram of a bandwidth extender of a
coding apparatus according to an exemplary embodiment of the
present invention.
[0117] The bandwidth extender 800 of the coding apparatus in FIG. 8
estimates the auxiliary information of the high band using the
encoded low band signal. The bandwidth extender 800 includes a
statistical model 801, a BWE estimator 803, and a feature vector
extractor 805.
[0118] In the bandwidth extender 800, the input low band signal is
fed to the feature vector extractor 805. The feature vector
extractor 805 generates a feature vector of the input low band
signal and provides the feature vector to the BWE estimator 803.
The BWE estimator 803 outputs the estimated high band signal using
the statistical model 801 pre-learned and required for the BWE
estimation and the input low band feature vector.
[0119] FIG. 9 is a flowchart for increasing coding efficiency by
predicting a high band signal at an encoder according to an
exemplary embodiment of the present invention.
[0120] After predicting the high band signal (referred to as a
first prediction signal) using the pre-encoded high band signal in
step 901, the encoder predicts the high band signal (referred to as
a second prediction signal) using the low band signal in step
903.
[0121] The encoder generates the residual high band signal by
subtracting the second prediction signal from the first prediction
signal in step 905, and encodes and transmits the generated
residual band signal in step 907.
[0122] Next, the encoder finishes this process.
[0123] FIG. 10 is a flowchart for increasing coding efficiency by
predicting a high band signal at a decoder according to an
exemplary embodiment of the present invention.
[0124] The decoder receives the encoded residual high band signal
from the encoder in step 1001 and decodes the received residual
high band signal in step 1003.
[0125] The decoder predicts the high band signal (referred to as a
first prediction signal) using the pre-decoded high band signal in
step 1005 and predicts the high band signal (referred to as a
second prediction signal) using the low band signal in step
1007.
[0126] Next, the decoder reproduces the original signal by adding
the first prediction signal and the second prediction signal in
step 1009 and then finishes this process.
[0127] So far, the apparatus and the method for predicting the high
band signal using the predictor to raise the coding efficiency at
the coding apparatus according to an exemplary embodiment of the
present invention have been explained. The coding efficiency can be
enhanced by connecting the predictor in serial or in parallel.
[0128] FIG. 11 includes graphs illustrating performance of a coding
apparatus according to an exemplary embodiment of the present
invention.
[0129] FIG. 11A is a graph illustrating performance of a coding
apparatus using serial Predictive Vector Quantization and Bandwidth
Extension (serial PVQ+BWE) according to an exemplary embodiment of
the present invention.
[0130] FIG. 11B is a graph illustrating performance of a coding
apparatus using parallel Predictive Vector Quantization and
Bandwidth Extension (parallel PVQ+BWE) according to an exemplary
embodiment of the present invention.
[0131] In the coding apparatus according to an exemplary embodiment
of the present invention, it is assumed that the low band signal is
converted with the 15.sup.th order MFCC feature vector, that is,
X={X1, . . . , X18} and the high band signal is converted with the
4.sup.th order MFCC={Y1, . . . , Y4}, instead of the PCM
signal.
[0132] In coding the two-dimensional high band vector {Y1, Y2},
Table 5 compares the coding performance of the coding apparatus
(the serial PVQ+BWE) with the serially connected predictor which
predicts the high band signal and the general coding apparatus (the
PVQ). FIG. 11A shows the results of Table 5.
TABLE-US-00005 TABLE 5 Quantization bits PVQ (CD value) Serial BWE
+ PVQ (CD value) 0 0.999994657 0.676158151 1 0.558172709
0.345071924 2 0.256129702 0.150522626 3 0.096594486 0.069829431 4
0.04251647 0.033419306 5 0.021238896 0.016838908 6 0.010677779
0.008480092 7 0.0053574 0.004279931 8 0.002699052 0.002155239
[0133] CD denotes the Cepstral Distance value.
[0134] In FIG. 11A, the coding apparatus exhibits coding efficiency
of about 0.5 bits per 20 ms frame at the low bit rate and about 25
bits per second.
[0135] In coding the two-dimensional high band vector {Y1, Y2},
Table 6 compares the coding performance between the coding
apparatus (the parallel PVQ+BWE) with the predictor connected in
parallel which predicts the high band signal and the general coding
apparatus (the PVQ). FIG. 11B shows the results of Table 6.
TABLE-US-00006 TABLE 6 Quantization bits PVQ (CD value) Parallel
BWE + PVQ (CD value) 0 0.999994657 0.553803491 1 0.558172709
0.239484191 2 0.256129702 0.116304886 3 0.096594486 0.058068495 4
0.04251647 0.029213927 5 0.021238896 0.014755009 6 0.010677779
0.00754634 7 0.0053574 0.003828885 8 0.002699052 0.001913953
[0136] CD denotes the Cepstral Distance value.
[0137] In FIG. 11B, the coding apparatus exhibits coding efficiency
of about 1 bit per 20 ms frame at the low bit rate and about 50
bits per second.
[0138] As such, the coding apparatus can predict and encode the
high band signal using the scalar scheme or the vector scheme
according to the purpose of the application.
[0139] FIG. 12 is a block diagram of an encoder of a portable
terminal according to an exemplary embodiment of the present
invention.
[0140] The encoder of FIG. 12 may include a high band mutual
information filter 1201, a quantizer 1203, a filter factor
calculator 1205, a high band signal estimator 1207, a low band
mutual information filter 1209, a low band encoder 1211, a low band
decoder 1213, and a high band mutual information inverse filter
1215.
[0141] The low band encoder 1211 processes to encode and transmit
the low band signal over the communication channel, and enables the
high band signal estimator 1207 to estimate the high band signal
using the encoded low band signal.
[0142] The low band mutual information filter 1209 increases the
mutual information of the encoded low band signal using the filter
factor provided from the filter factor calculator 1205.
[0143] The high band mutual information filter 1201 converts the
input high band signal using the filter factor provided from the
filter factor calculator 1205. That is, the high band mutual
information filter 1201 converts the pre-received high band signal
(a first high band signal) to the output high band signal (a second
high band signal) with the increased mutual information.
[0144] The filter factor calculator 1205 determines the low band
filter factor and the high band filter factor required to increase
the mutual information of the two input signals using the decoded
high band signal provided from the high band mutual information
inverse filter 1215 and the low band signal decoded by the low band
decoder 1213, and provides the factors to the respective
filters.
[0145] Herein, the decoded high band signal provided from the high
band mutual information inverse filter 1215 includes the fed back
signal which is decoded from the encoded high band signal of the
previous frame, and the decoded low band signal is the signal
decoded from the encoded low band signal of the current frame.
[0146] The encoder processes to output the residual high band
signal (the second residual high band signal) by subtracting the
high band signal (the second high band signal) converted by the
high band mutual information filter 1201 and the high band signal
estimated by the high band signal estimator 1207, and controls the
quantizer 1203 to quantize the signal.
[0147] FIG. 13 is a block diagram of a decoder of a portable
terminal according to an exemplary embodiment of the present
invention.
[0148] The decoder of FIG. 13 includes a dequantizer 1301, a high
band mutual information inverse filter 1303, a filter factor
calculator 1305, a high band signal estimator 1307, a low band
mutual information filter 1309, and a low band decoder 1311.
[0149] The low band decoder 1311 decodes the encoded low band
signal and enables the high band signal estimator 1307 to estimate
the high band signal using the decoded low band signal.
[0150] The dequantizer 1301 receives and de-quantizes the encoded
residual high band signal (the second encoded residual high band
signal) and outputs the decoded residual high band signal (the
second decoded residual high band signal).
[0151] The filter factor calculator 1305 determines a low band
filter factor and a high band inverse filter factor using the
decoded high band signal and the decoded low band signal, and
provides the factors to the respective filters. Herein, the low
band filter factor determined at the filter factor calculator 1305
is the same as the low band filter factor of the transmitter with
respect to the same frame, and the high band filter inverse filter
factor is the same as the high band inverse filter factor of the
transmitter and has an inverse relation with the high band filter
factor of the transmitter.
[0152] The low band mutual information filter 1309 increases the
mutual information of the decoded low band signal using the factor
provided from the filter factor calculator 1305 and provides the
decoded low band signal to the high band signal estimator 1307 to
estimate the high band signal.
[0153] Hence, the decoder adds the residual high band signal
decoded by the dequantizer 1301 and the high band signal estimated
by the high band signal estimator 1307 and outputs the decoded high
band signal (the second decoded high band signal) to the high band
mutual information inverse filter 1303.
[0154] The high band mutual information inverse filter 1303
inversely filters the decoded high band signal (the second decoded
high band signal) using the inverse filter factor provided from the
filter factor calculator 1305 and processes to reproduce the
original high band signal.
[0155] FIG. 14 is a block diagram of a filter factor calculator
applied to an encoder according to an exemplary embodiment of the
present invention.
[0156] The filter factor calculator 1400 applied to the encoder in
FIG. 14 includes a high band mutual information filter factor
calculator 1401 and a low band mutual information filter factor
calculator 1403.
[0157] The high band mutual information filter factor calculator
1401 determines the factor of the high band mutual information
filter. The high band mutual information filter factor calculator
1401 can determine the factor using the decoded high band signal
and the decoded low band signal.
[0158] The low band mutual information filter factor calculator
1403 determines the factor of the low band mutual information
filter. The low band mutual information filter factor calculator
1403 can determine the factor using the decoded high band signal
and the decoded low band signal.
[0159] To determine the filter factor for increasing the mutual
information of the high band signal, the filter factor calculator
1400 of the encoder should meet the following conditions.
[0160] It is assumed that the low band signal is X, the high band
signal is Y, the high band mutual information filter is H[ ], the
high band mutual information inverse filter is H.sup.-1[ ], and the
high band signal converted by H[ ] is Y2.
[0161] First, H[ ] should be reversible, and H.sup.-1[ ] should
exist to establish Y=H.sup.-1[Y2]=H.sup.-1[H[Y]]. That is, it
should be possible to reproduce the original signal Y from the
converted signal Y2.
[0162] Second, the mutual information I[X;Y2]>I[X;Y] should be
established.
[0163] Third, the dynamic range of Y2 should not be greater than at
least that of Y in the statistical sense.
[0164] The conditions to be satisfied in the filter factor
calculation shall be described in more detail by referring to FIG.
16.
[0165] FIG. 15 is a block diagram of a filter factor calculator of
a decoder according to an exemplary embodiment of the present
invention.
[0166] The filter factor calculator 1500 applied to the decoder in
FIG. 15 includes a high band mutual information inverse filter
factor calculator 1501 and a low band mutual information filter
factor calculator 1513.
[0167] The high band mutual information inverse filter factor
calculator 1501 determines the factor of the high band mutual
information inverse filter. The high band mutual information
inverse filter factor calculator 1501 can determine the factor
using the decoded high band signal and the decoded low band
signal.
[0168] The low band mutual information filter factor calculator
1513 determines the factor of the low band mutual information
filter. The low band mutual information filter factor calculator
1513 can determine the factor using the decoded high band signal
and the decoded low band signal.
[0169] Herein, the filter factor calculator 1500 of the decoder
should determine the filter factors to increase the mutual
information of the high band signal while satisfying the conditions
as in the filter factor calculator 1400 of the encoder as described
earlier with respect to FIG. 14.
[0170] So far, the apparatuses for controlling the correlation (the
mutual information) affecting the coding efficiency in the coding
apparatus of the portable terminal using the BWE have been
described. Now, explanations are provided regarding methods for
controlling the correlation (the mutual information) affecting the
coding efficiency using the apparatuses according to exemplary
embodiments of the present invention.
[0171] FIG. 16 is a flowchart illustrating operations of an encoder
according to an exemplary embodiment of the present invention.
Herein, the encoder performs the artificial BWE on the high band of
the input signal to increase the mutual information between the
high band and the low band. Accordingly, the encoder encodes the
low band signal using the low band encoder and outputs the encoded
low band signal.
[0172] The encoder determines the mutual information filter factors
in step 1601 and converts the input high band signal (the first
high band signal) using the determined filter factors in step 1603.
Herein, the mutual information filter factors include the factor of
the high band mutual information filter and the factor of the low
band mutual information filter, which are determined at the filter
factor calculator. The converted high band signal (the second high
band signal) indicates the output high band signal with the
increased mutual information, relative to the input high band
signal.
[0173] The filter factor calculator should meet the following
conditions.
[0174] It is assumed that the low band signal is X, the high band
signal is Y, the high band mutual information filter is H[ ], the
high band mutual information inverse filter is H.sup.-1[ ], and the
high band signal converted by H[ ] is Y2.
[0175] First, H[ ] should be reversible, and H.sup.-1[ ] should
exist to establish Y=H.sup.-1[Y2]=H.sup.-1[H[Y]]. That is, it
should be possible to reproduce the original signal Y from the
converted signal Y2.
[0176] Second, the mutual information I[X;Y2]>I[X;Y] should be
established.
[0177] Third, the dynamic range of Y2 should not be greater than at
least that of Y in the statistical sense.
[0178] The first condition implies that the signal converted by the
high band mutual information filter of the transmitter should be
recovered by the high band mutual information inverse filter of the
receiver, and the second and third conditions imply that the
conversion by the filter H[ ] should contribute to the enhancement
of the coding efficiency.
[0179] As for the first condition, that is, as for H.sup.-1[ ], the
filter H[ ] fundamentally represents a monotonic and differentiable
function, whereas the mutual information does not change for the
conversion function. That is, I[X;Y2]=I[X;Y], which cannot meet the
second condition.
[0180] To address this problem, exemplary embodiments of the
present invention introduce the expression "reversible" to define
the function which ultimately enables reproduction of the original
transmit information Y using the other transmit information, e.g.,
using the low band vector X.
[0181] For example, Y2=H[X,Y]=X*={x.sub.1y.sub.1, . . . ,
x.sub.Ny.sub.N}'. * denotes the multiplication between the
components. x.sub.1 and y.sub.1 denote the components of X and Y.
The inverse function H.sup.-1[ ], that is, the function of
reproducing Y from Y2 with the given X can be defined as
Y=H.sup.-1[X,Y2]=X/2,={x.sub.1/y2.sub.1, . . . , x.sub.N/y2.sub.N}.
/ denotes the division between the components and x.sub.1 and
y2.sub.1 denote the components of X and Y2.
[0182] Y2, sent from the transmitter using the function *, can be
recovered to Y at the receiver using the function /. As for the
second condition, when the two random variables (or vectors) have
mutual dependence, that is, the mutual function relation, their
mutual information generally increases. In other words, when Y2
converted by the filter H[ ] has a certain function relation with
X, e.g., the function relation of Y2=f[X], the mutual information
of the two random vectors Y2 and X increases.
[0183] Next, the encoder controls the low band mutual information
filter to estimate the high band signal in step 1605 and processes
to output the residual high band signal (the second residual high
band signal) in step 1607.
[0184] Herein, the residual high band output signal is produced by
subtracting the high band signal (the second high band signal)
converted in step 1603 and the high band signal estimated in step
1605.
[0185] In step 1609, the encoder quantizes the residual signal and
transmits the quantized residual signal (the second encoded
residual high band signal) over the communication channel. Herein,
the quantizer for quantizing the residual signal can employ a
scalar or vector quantizer according to the purpose of the
application.
[0186] Next, the encoder finishes this process.
[0187] FIG. 17 is a flowchart illustrating operations of a decoder
according to an exemplary embodiment of the present invention.
Herein, the decoder processes to decode the input signal with the
increased mutual information between the high band and the low
band. The decoder controls the low band decoder to decode the
encoded low band signal received in the communication channel and
reproduces the low band signal.
[0188] In step 1701, the decoder receives the residual signal (the
second encoded residual high band signal) of the high band
converted by the encoder.
[0189] The decoder quantizes the received residual signal in step
1703 and decodes to the high band signal in step 1705. In more
detail, the decoder outputs the second encoded residual high band
signal received, as the second decoded residual high band
signal.
[0190] In step 1707, the decoder determines the filter factors
using the decoded signal. Herein, the filter factors include the
low band filter factor and the high band inverse filter factor. The
decoder can determine the filter factors using the decoded high
band signal and the decoded low band signal. The low band filter
factor is the same as the low band filter factor of the transmitter
in the same frame, and the high band inverse filter factor is the
same as the high band inverse filter factor of the transmitter and
has the inverse relation with the high band filter factor of the
transmitter.
[0191] In step 1709, the decoder decodes to the original high band
signal.
[0192] The decoding to the original high band signal reproduces the
decoded high band signal (the second decoded high band signal) by
adding the second residual high band signal decoded in step 1705
and the high band signal estimated by the high band signal
estimator, inversely filters the decoded high band signal, and
decodes to the original high band signal.
[0193] Next, the decoder finishes this process.
[0194] FIG. 18 is a flowchart of a method for determining filter
factors at a filter factor calculator according to an exemplary
embodiment of the present invention.
[0195] The filter factor calculator confirms the decoded high band
signal of the previous frame in step 1801 and determines the high
band filter factor in step 1803. More specifically, the filter
factor calculator determines the filter for increasing the mutual
information of the input high band signal by use of the decoded
high band signal of the previous frame.
[0196] The filter factor calculator confirms the decoded low band
signal in step 1805 and determines the low band filter factor in
step 1807. Herein, the filter factor calculator determines the
filter for increasing the mutual information of the input signal
using the decoded low band signal which is the decoded signal of
the encoded low band signal of the current frame.
[0197] Next, the filter factor calculator finishes this
process.
[0198] While an exemplary apparatus and method for increasing the
mutual information of the high band signal and the low band signal
utilize the filter factor of the high band signal and the filter
factor of the low band signal, the mutual information of the high
band signal and the low band signal can be raised by applying only
one of the high band mutual information filter and the low band
mutual information filter.
[0199] The method for adopting only the high band mutual
information filter or only the low band mutual information filter
is substantially the same as the method using both of the high band
mutual information filter and the low band mutual information
filter in FIGS. 2 through 8, but can increase the mutual
information of the high band signal and the low band signal merely
using either filter.
[0200] FIG. 19 includes graphs illustrating performance of a
decoder according to an exemplary embodiment of the present
invention.
[0201] As stated earlier, an exemplary method for increasing the
mutual information of the high band vector and the low band vector
can employ both or only one of the high band mutual information
filter and the low band mutual information filter.
[0202] In FIG. 19, an exemplary method employing only the high band
mutual information filter and an exemplary method employing only
the low band mutual information filter are illustrated.
[0203] FIG. 19A is a graph comparing performance of an exemplary
coding apparatus employing only a high band mutual information
filter and a conventional coding apparatus. FIG. 19B is a graph
comparing performance of an exemplary coding apparatus employing
only the low band mutual information filter and a conventional
coding apparatus.
[0204] To compare performance of the coding apparatus of a
conventional portable terminal and a coding apparatus according to
an exemplary embodiment of the present invention, the low band
signal of the PCM voice signal sampled at 16 kHz is converted to
the 14.sup.th order MFCC feature vector and log scaled energy, that
is, to X(n)={x1(n), . . . , x14(n), InE.sub.LB(n)}, and the
corresponding high band signal is converted to the 4.sup.th order
MFCC factor and the log scaled energy, that is, to Y(n)={y1(n), . .
. , y4(n), InE.sub.HB(n)}'. n denotes a frame number and the frame
size is 20 ms. In this situation, the coding issue is to code the
4.sup.th order high band MFCC and the energy information Y(n) with
efficiency.
[0205] Prior to the operations of the coding apparatus employing
only the high band mutual information filter, provided that the
coding apparatus codes only E.sub.HB of the high band signal in
Y(n) information, the high band signal is Y(n)={InE.sub.HB(n)}. An
exemplary high band mutual information filter for converting the
original high band signal Y(n) to Y2(n) can be expressed as
Equation (2).
Y2(n)=H[X(n),Y(n-1)]=InE.sub.HB(n)-InE.sub.LB(n)=In(E.sub.HB(n)/E.sub.LB-
(n)) (2)
[0206] In Equation (2), X denotes the low band signal, Y denotes
the high band signal, H[ ] denotes the high band mutual information
filter, Y2 denotes the high band signal converted by H[ ], E.sub.HB
denotes the energy of the high band signal, and E.sub.LB denotes
the energy of the low band signal. Y(n-1) denotes the encoded high
band vector of the (n-1)-th frame fed back.
[0207] In Equation (2), the high band mutual information filter
corresponds to the differential operation in the log scale and to
the division in the linear scale.
[0208] The high band mutual information filter meets the first
condition (that H[ ] should be reversible and H.sup.-1[ ] should
exist to establish Y=H.sup.-1[Y2]=H.sup.-1[H[Y]], that is, it
should be possible to reproduce the original signal Y from the
converted signal Y2) of the three conditions aforementioned.
Namely, the original high band signal can be restored from the high
band signal Y2 converted by the high band mutual information filter
and the component InE.sub.LB (n) of the low band signal (X(n)),
which is expressed as Equation (3).
InE.sub.HB(n)=Y2(n)+InE.sub.LB(n) (3)
[0209] In Equation (3), E.sub.HB denotes the energy of the high
band signal, E.sub.LB denotes the energy of the low band signal,
and Y2 denotes the high band signal converted by the high band
mutual information filter.
[0210] Equation (2) meets the second condition (that the mutual
information I[X;Y2]>I[X;Y] should be established) of the three
conditions based on Equation (4).
I[X(n);Y2(n)]=1.27>I[X(n);Y(n)]=0.71 (4)
[0211] In Equation (4), X denotes the low band signal, Y denotes
the high band signal, and Y2 denotes the high band signal converted
by the high band mutual information filter.
[0212] In Equation (4), the mutual information of Y2 increases by
about 0.56 bit, compared to the mutual information of Y, which
implies the enhancement of the coding efficiency of 0.56 bit per
frame and 28 bits per second in the coding of the high band energy
Y(n)={InE.sub.HB(n)}. The variance of Y is about 74.44 and the
variance of Y2 is about 35.06. Thus, Equation (2) meets the third
condition (that the dynamic range of Y2 should not be greater than
at least that of Y in the statistical sense).
[0213] The mutual information between the two vectors in Equation
(4) can be expressed as Equation (5).
I ( X ; Y ) = .intg. .OMEGA. y .intg. .OMEGA. x f X , Y ( x , y )
log 2 ( f X , Y ( x , y ) f X ( y ) f Y ( y ) ) ( 5 )
##EQU00002##
[0214] In Equation (5), X denotes the feature vector of the low
band signal and Y denotes the feature vector of the high band
signal. f.sub.X(x) denotes a probability density function of X,
f.sub.Y(y) denotes a probability density function of Y, and
f.sub.XY(x, y) denotes a joint probability density function of X
and Y.
[0215] As above, the filter defined in Equation (2) satisfies all
of the three conditions as the high band mutual information filter
and raises the coding efficiency of the high band energy
Y(n)={InE.sub.HB(n)}.
[0216] Table 7 compares the performance of a conventional coding
apparatus (BWE) and an exemplary embodiment of the present
invention (eBWE), and FIG. 19A illustrates performance of an
exemplary coding apparatus employing only the high band mutual
information filter and a conventional coding apparatus.
TABLE-US-00007 TABLE 7 Quantization bits BWE eBWE 0 74.44139682
35.04823669 1 29.9638428 14.41622256 2 10.48636178 4.902777868 3
3.237544251 1.483840889 4 0.879504628 0.412519595 5 0.228972655
0.108508489 6 0.058430905 0.028144785 7 0.014838623 0.007102297 8
0.003612276 0.001717147
[0217] The values in Table 7 indicate the coding error energy,
which implies that the exemplary coding apparatus improves the
coding performance further than the general coding apparatus.
[0218] Operations of another exemplary coding apparatus employing
only the low band mutual information filter are described now.
[0219] Prior to the exemplary method for raising the coding
efficiency by employing only the low band mutual information
filter, provided that the coding apparatus codes only the 4.sup.th
order MFCC of the high band signal in Y(n) information, the high
band signal is Y(n)={y1(n), . . . , y4(n)}. An exemplary low band
mutual information filter for converting the original low band
signal X(n) to X2(n) can be expressed as Equation (6).
X2(n)=G[X(n),Y(n-1)]={X(n):Y(n-1)}'={x.sub.1(n), . . .
,x.sub.14(n):y.sub.1(n-1), . . . ,y.sub.4(n-1)}' (6)
[0220] In Equation (6), X denotes the low band signal, Y denotes
the high band signal, G[ ] a denotes the low band mutual
information filter, X2 denotes the low band signal converted by G[
], : denotes an augmentation operator in the matrix and the vector,
and Y(n-1) denotes the encoded high band vector of the (n-1)-th
frame fed back.
[0221] The low band mutual information filter in Equation (6)
indicates the augmentation operator which outputs an augmented
vector.
[0222] The low band mutual information filter satisfies the second
of the three necessary conditions of the present mutual information
filter. The mutual information increases by the augmented vector X2
based on Equation (7).
[0223] According to the mutual information computation based on
Equation (7), as the low band signal is changed from X to X2, the
mutual information increases by approximately 1 bit. This predicts
the enhancement of the coding efficiency of 1 bit per frame and 50
bits per second when the 4.sup.th order high band MFCC Y is coded.
The first and third of the three necessary conditions of the
present mutual information filter relate to the high band mutual
information filter. When the low band mutual information filter
alone is employed, the first and third conditions do not apply.
[0224] Table 8 compares performance of a conventional coding
apparatus (BWE) and an exemplary coding apparatus (eBWE), and FIG.
19B illustrates performance of an exemplary coding apparatus
employing only the low band mutual information filter and a
conventional coding apparatus.
TABLE-US-00008 TABLE 8 Quantization bits BWE (CD) eBWE (CD) 2
0.410244 0.3954 3 0.293181 0.260144 4 0.21433 0.176756 5 0.155101
0.122713 6 0.112254 0.0866 7 0.081301 0.061116 8 0.058495
0.043185
[0225] The values in Table 8 indicate the cepstral distance values,
which imply that the coding apparatus according to an exemplary
embodiment of the present invention improves the coding performance
further than the general coding apparatus.
[0226] As set forth above, in a portable terminal which encodes and
decodes voice and audio signals using the artificial BWE, the
signal is coded by removing information indicative of the
characteristic of the high band signal of the signal to be coded.
Therefore, an improved coding performance can be accomplished, as
compared to the conventional coding apparatus using the BWE.
[0227] While the invention has been shown and described with
reference to certain exemplary embodiments thereof, it will be
understood by those skilled in the art that various changes in form
and details may be made therein without departing from the spirit
and scope of the invention as defined by the appended claims and
their equivalents.
* * * * *